Generally, an ink jet recording apparatus includes a carriage on which an ink jet recording head having a pressure generating means that pressurizes a pressure generating chamber, and a nozzle opening from which the pressurized ink is ejected as an ink droplet is mounted; and an ink tank which houses ink to be supplied through a flowing path to the recording head. The ink jet recording apparatus is constituted so that continuous printing can be performed.
Here, the ink tank is constituted generally as a cartridge that is detachable from the recording apparatus so that a user can easily exchange it when the ink has been used up.
As methods of managing ink consumption of a conventional ink cartridge, there have been known a method of managing ink consumption on calculation by adding up the count number of the ink droplets ejected by the recording head, and the quantity of ink absorbed in a maintenance process of a print head by use of software; and a method of managing ink consumption by detecting, by attaching two electrodes for directly detecting a liquid level to the ink cartridge, the time when the predetermined quantity of ink has been actually consumed.
However, in the method of managing the ink consumption on calculation by adding up the ejection number of the ink droplets and the quantity of the absorbed ink by use of software, depending on environments of use, for example, by rise and fall of temperature or humidity in a using room, the elapse time since opening of the ink cartridge, and difference of a using frequency on user's side, pressure in the ink cartridge and viscosity of ink change. Therefore, there is a problem that an error that is not negligible is produced between the ink consumed quantity on calculation and the actual ink consumed quantity. Further, by individual difference of the ink jet head, the ink quantity per dot varies, thereby to also cause the problem that an error is produced between the ink consumed quantity on calculation and the actual ink consumed quantity. Further, in case that a cartridge is once detached and the same cartridge is attached again, the added count value is once reset, so that there is also a problem that the actual ink level is unclear.
On the other hand, in the method of managing the time when the ink has been consumed by the electrodes, the actual quantity in a point of the ink consumption can be detected. Therefore, the ink level can be managed with high reliability. However, in order to detect liquid level of ink, the ink must be conductive, so that the kind of used ink is limited. Further, there is a problem that liquid closeness structure between the electrode and the ink cartridge is complicated. Further, since the precious metal that is good in conductivity and also high in corrosion resistance is usually used as a material of the electrode, there is also a problem that the manufacturing cost of the ink cartridge increases. Further, since the two electrodes must be attached respectively to the different positions of the ink cartridge, there is also a problem that a manufacturing process is complicated thereby to cause the increase of the manufacturing cost.
On the contrary, an ink level detecting unit has been also proposed, which detects existence of the ink on the basis of a residual vibration frequency of a vibration element such as a piezoelectric element. Namely, the residual vibration frequency of the vibration element such as the piezoelectric element, when the vibration element such as the piezoelectric element and a medium (ink, air or the like) that comes into contact with this vibration element are in a resonant state, means a resonant frequency between the vibration element such as the piezoelectric element and the medium that comes into contact with this vibration element. In the above ink level detecting unit, the state of the ink that is the medium is detected by change of this resonant frequency.
In widely various electronic apparatuses, from a viewpoint of energy-saving, a tendency to set a drive voltage low is spreading. In an ink jet printer, also, the need of making the drive voltage low is increasing.
In the above ink level detecting unit, conventionally, the piezoelectric element is pulse-driven at the drive voltage of, for example, 5V thereby to find the above residual vibration frequency.
However, with lowering of the drive voltage, in case that the drive voltage of the above piezoelectric element is set, for example, at 3.3V, the vibration applied to the piezoelectric element becomes small because of lowering of the drive voltage. Therefore, the amplitude of the above residual vibration becomes also small, so that the level of the detection signal by this residual vibration lowers.
Therefore, in case that the existence of the ink in the ink tank is detected on the basis of the detection signal of this residual vibration, since the level of the detection signal lowers, the ink level detecting unit is easy to receive influences such as noise by motors of the ink jet recording apparatus or noise by inducement of a head drive waveform. As described above, the ink level detecting unit which detects the existence of the ink on the basis of the residual vibration frequency of the vibration element is sensitive to the noise, so that there is a problem that detection accuracy lowers under the environment in which the noise is large, and the detection becomes difficult occasionally.
Further, in such the ink level detecting unit, when the position of the liquid level of the ink is nearly equal to the position of the vibration element such as the piezoelectric element that functions as a sensing element (when the liquid level is in a boundary region of ink presence and ink absence), in case that foaming and waving of the liquid level of the ink are produced with movement of the carriage, there is fear of erroneous detection on the existence of ink.
Therefore, an object of the invention is to provide ink level detecting technology of an ink jet recording apparatus in which excitation is applied to a vibration element such as a piezoelectric element, and residual vibration by resonance between the vibration element and a medium such as ink that comes into contact with the vibration element is surely detected without receiving an influence of noise, thereby to increase ink detecting accuracy and reliability.
Further, another object of the invention is to provide ink level detecting technology of an ink jet recording apparatus in which excitation is applied to a vibration element such as a piezoelectric element, and it is possible to prevent residual vibration by resonance between the vibration element and a medium such as ink that comes into contact with the vibration element, also in case that foaming and waving of a liquid level of ink are produced by movement of a carriage, from being detected erroneously.